The objective of this study will be to develop a mathematical model for the asymmetric branching pattern of bronchi in the human lung. The investigator will organize the disparate theories of form, dimension, and growth developed independently by authors in geology, neurology, botany and physiology. Models based on random growth and optimal design will be developed mathematically, fitted numerically, and tested statistically against computer-stored data on human and animal lungs. The sought-for model of the human lung will incorporate quantitative principles of topological, mechanical, and physiological design inherent in the branching structure, and will be applicable as a practical tool for calculation of variables of respiratory mechanics. Comparison of the principles and numerical parameters of design will be made between regions of the human lung, and between animal lungs and human lungs.